Analysis of the Effect of the Oxide Ion Vacancy on the Crystal Structure of La1-xCaxCrO3-δ by High-Temperature X-Ray Diffraction under Various Oxygen Partial Pressures

2005 ◽  
Vol 242-244 ◽  
pp. 9-16 ◽  
Author(s):  
Norifumi Ohba ◽  
Eri Oikawa ◽  
Takuya Hashimoto
Keyword(s):  
High Temperature ◽  
Solution Model ◽  
Ideal Solution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lattice Constants ◽  
Expansion Behavior ◽  
Partial Pressures ◽  
Increasing Temperature ◽  
Oxide Ion

In order to evaluate potential of La1-xCaxCrO3-δ as a material for interconnector of solid oxide fuel cells, reduction expansion was measured by using high temperature X-ray diffraction under various P(O2). Obtained reduction expansion increased with increasing temperature and Ca content. With combination of obtained lattice constants and oxygen nonstoichiometry data, the effect of oxide ion vacancy on crystal lattice and their thermodynamic behavior have been deduced. It was proposed that expansion behavior by δ of La0.9Ca0.1CrO3-δ can be explained assuming ideal solution model on oxide ion vacancies, however, deviation from ideal solution model was observed in reduction expansion behavior of La0.8Ca0.2CrO3-δ and La0.7Ca0.3CrO3-δ with δ region larger than 0.03 and 0.05, respectively. It was revealed that the crystal system approached to cubic with increase of δ in the region where the deviation from ideal solution model was observed.

Microstructural Evolution during High-Temperature Oxidation of Ti2AlN Ceramics

2010 ◽  
Vol 65 ◽  
pp. 106-111
Author(s):  
Bai Cui ◽  
Rafael Sa ◽  
Daniel Doni Jayaseelan ◽  
Fawad Inam ◽  
Michael J. Reece ◽  
...  
Keyword(s):  
High Temperature ◽  
Microstructural Evolution ◽  
High Temperature Oxidation ◽  
Oxidation Mechanism ◽  
X Ray Diffraction ◽  
Temperature Oxidation ◽  
X Ray ◽  
Oxidation In Air ◽  
Α Al2o3 ◽  
Increasing Temperature

Microstructural evolution of Ti2AlN ceramics during high-temperature oxidation in air has been revealed by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), and energy-dispersive spectroscopy (EDS). After oxidation below 1200 °C, layered microstructures formed on Ti2AlN surfaces containing anatase, rutile, and α-Al2O3. Above 1200 °C, more complex layered microstructures formed containing Al2TiO5, rutile, α-Al2O3, and continuous void layers. With increasing temperature, anatase gradually transformed to rutile, and TiO2 reacted with α-Al2O3 to form Al2TiO5. Based on these microstructural observations, an oxidation mechanism for Ti2AlN ceramics is proposed.

scholarly journals Synthesis, Structure and Thermophysical Properties of Phosphates MNi0.5Zr1.5(PO4)3 (M = Mg, Ca, Sr)

2010 ◽  
Vol 12 (3,4) ◽  
pp. 241 ◽  
Author(s):  
M.V. Sukhanov ◽  
I.A. Schelokov ◽  
V.I. Pet'kov ◽  
E.R. Gobechiya ◽  
Yu.K. Kabalov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Heat Capacity ◽  
Thermal Expansion ◽  
High Temperature ◽  
Single Phase ◽  
Rietveld Method ◽  
Type Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Expansion Behavior

<p>New phosphates MNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> (M = Mg, Ca, Sr) were prepared by the precipitating method.<strong><em> </em></strong>Phosphates were characterized using X-ray powder diffraction, IR-spectroscopy and electron microprobe analyses. The crystal structure of phosphates was refined by the Rietveld method. Phosphates CaNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> and SrNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> are shown to have been crystallized in the NaZr<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>-type structure and the phosphate MgNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3 </sub>was obtained as a single-phase with Sc<sub>2</sub>(WO<sub>4</sub>)<sub>3</sub>-type structure. Heat capacity of phosphate CaNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> was measured in the range 7 – 650 K and increased monotonically over the entire temperature range studied. Thermal expansion of phosphate CaNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> was studied in the interval 295-1073 K by the high temperature X-ray diffraction. This phosphate is similar to the best low-expansion ceramics, such as zircon, cordierite and silica glass in thermal expansion behavior.</p>

scholarly journals An Experimental Study of the Formation of Talc through CaMg(CO3)2–SiO2–H2O Interaction at 100–200°C and Vapor-Saturation Pressures

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Ye Wan ◽  
Xiaolin Wang ◽  
I-Ming Chou ◽  
Wenxuan Hu ◽  
Yang Zhang ◽  
...  
Keyword(s):  
Low Temperatures ◽  
Fused Silica ◽  
X Ray Diffraction ◽  
In Situ Raman Spectroscopy ◽  
X Ray ◽  
In Situ Raman ◽  
Geological Processes ◽  
Partial Pressures ◽  
Increasing Temperature

The metamorphic interaction between carbonate and silica-rich fluid is common in geological environments. The formation of talc from dolomite and silica-rich fluid occurs at low temperatures in the metamorphism of the CaO–MgO–SiO2–CO2–H2O system and plays important roles in the formation of economically viable talc deposits, the modification of dolomite reservoirs, and other geological processes. However, disagreement remains over the conditions of talc formation at low temperatures. In this study, in situ Raman spectroscopy, quenched scanning electron microscopy, micro-X-ray diffraction, and thermodynamic calculations were used to explore the interplay between dolomite and silica-rich fluids at relatively low temperatures in fused silica tubes. Results showed that talc formed at ≤200°C and low CO2partial pressures (PCO2). The reaction rate increased with increasing temperature and decreased with increasingPCO2. The major contributions of this study are as follows:(1)we confirmed the formation mechanism of Mg-carbonate-hosted talc deposits and proved that talc can form at ≤200°C;(2)the presence of talc in carbonate reservoirs can indicate the activity of silica-rich hydrothermal fluids; and (3) the reactivity and solubility of silica require further consideration, when a fused silica tube is used as the reactor in highP–Texperiments.

High temperature x-ray and calorimetric studies of phase transformations in quasicrystalline Ti–Zr–Ni alloys

1997 ◽  
Vol 12 (2) ◽  
pp. 434-438 ◽  
Author(s):  
R. M. Stroud ◽  
K. F. Kelton ◽  
S. T. Misture
Keyword(s):  
High Temperature ◽  
Alloy Composition ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Ni Alloys ◽  
Partial Pressures ◽  
Calorimetric Studies

We present the first high temperature x-ray diffraction (HTXRD) studies of in situ quasicrystal-crystal and crystal-crystal transformations in Ti–Zr–Ni alloys. Together with differential scanning calorimetry studies, these x-ray measurements indicate three separate paths for the Ti–Zr–Ni quasicrystal-crystal transformation: single exothermic, single endothermic, or multiple endothermic. The mode of transformation depends on the alloy composition and the level of environmental oxygen. The crystalline products include the Ti2Ni, MgZn2 Laves, α−(Ti, Zr), and β−(Ti, Zr) phases. In the absence of oxygen, the endothermic transformation of the quasicrystal demonstrates that it is the lowest free energy (stable) phase at the Ti53Zr27Ni20 composition. Oxygen stabilizes the Ti2Ni phase, eliminating both the quasicrystal and the MgZn2 Laves phase, at partial pressures as low as a few hundred ppm.

Variation of cation distribution with temperature and its consequences on thermal expansion for Ca3Eu2(BO3)4

2020 ◽  
Vol 76 (4) ◽  
pp. 554-562
Author(s):  
Katarzyna M. Kosyl ◽  
Wojciech Paszkowicz ◽  
Alexey N. Shekhovtsov ◽  
Miron B. Kosmyna ◽  
Jerzy Antonowicz ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
High Resolution ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lattice Constants ◽  
Thermal Expansion Anisotropy ◽  
Structural Details

The structure of calcium europium orthoborate, Ca3Eu2(BO3)4, was determined using high-resolution powder X-ray diffraction data collected at the ID22 beamline (ESRF) under ambient conditions, as well as at high temperature. Rietveld refinement allowed determination of the lattice constants and structural details, including the Ca/Eu ratios at the three cationic sites and their evolution with temperature. Clear thermal expansion anisotropy was found, and slope changes of lattice-constant dependencies on temperature were observed at 923 K. Above this temperature the changes in occupation of the Ca/Eu sites occur, exhibiting a tendency towards a more uniform Eu distribution over the three Ca/Eu sites. Possible structural origins of the observed thermal expansion anisotropy are discussed.

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